In a petroleum refining process, bottom oil (atmospheric residue, AR) can be obtained by atmospheric distillation of crude petroleum. Each of the atmospheric residue and vacuum gas oil (VGO) obtained by vacuum distillation of the atmospheric residue is subjected to a desulfurization treatment or a catalytic cracking treatment, and thus products such as gasoline, lubricant base oil, or other chemicals can be obtained. Meanwhile, the vacuum residual oil obtained by the vacuum distillation of the atmospheric residue is a low-margin product compared to the above products. Accordingly, it is preferable to produce higher-margin products from the vacuum residual oil.
In the following Patent Literature 1, a technique is disclosed in which oil deasphalted by solvent (DAO: deasphalted oil) obtained by deasphalting of vacuum residual oil is mixed with atmospheric residue and/or vacuum gas oil, thereby preparing mixed oil, and the mixed oil is subjected to hydrorefining to produce a fuel such as gasoline.